Manufacture of noncurling multilayer material



United States Patent 2,993,793 MANUFACTURE OF NONCURLING MULTILAYER MATERIAL Jules Edmond Beersmans, Antwerp, and Polydoor Frans De Smet, Wilrijk-Antwerp, Belgium, assignors to Gevaert Photo-Producten N.V., Mortsel, Belgium, a Belgian company No Drawing. Filed Feb. 1'5, 1955, Ser. No. 488,429- Claims priority, application Great Britain Feb. 1 6, 1954 1 Claim. (Cl. 96--87) This invention relates to a process for manufacturing noncurling multilayer material, especially photographic material, such as films and papers.

It is known that a flexible flat support bearing a wet gelatin layer will curl toward the gelatin layer, while drying. Such curling is caused by the tendency of a gelatin gel to shrink on drying. The tensions hereby arising in the dry layer cause the curling of the multilayer material.

It is, thus, an object of our invention to make sure that a flexible multilayer material will stay flat.

Another object of the invention is to impart to gelatin layers which are to be applied to multilayer material enhanced anticurling properties.

A further object of our invention centers about multilayer material, such as, for instance, photographic films, which neither before nor during the treatment with aqueous solution, nor afterwards when drying, will curl so that the material may easily be worked.

Still further objects will appear from the following description.

The curling may be counteracted by applying to the side opposite to that bearing the gelatin layer another layer, the tensions of which will counteract those of the gelatin layer.

We have found that the control of the curling of multilayer material toward one side, by applying a gelatin layer to the opposite side, may easily be facilitated by incorporating in the gelatin layer organic and/or inorganic inert fillers in the form of finely divided insoluble solid particles. This may be elfected by applying to the multilayer material either a gelatin solution containing the inert particles, or a gelatin layer in which the inert particles are formed after coating the solution.

Our process makes it possible to modify the gelatin content of the anticurling layer by varying the amount of the solid particles.

Though the process according to our invention may be applied to all sorts of multilayer material, it is of primordial importance for the preparation of noncurling photographic material. By noncurling photographic ma terial, a material is meant which in a dry state before as well as after processing, and at atmospheres with varying moisture content, remains perfectly fiat, and which curls only a little during the treatment in developing and fixing baths and, above all, during drying.

The emulsion layer of a photographic material contains before as well as after processing finely divided solid particles consisting of silver halide and silver, respectively. In order to prevent the curling of a multilayer material bearing on one side a silver halide emulsion layer, a gelatin layer with a gelatin content higher than that of the emulsion layer should be applied to the other side. This process, among other disadvantages, has the. drawback that both layers do not dry simultaneously, which causes a strong curling action during drying.

The process according to our invention offers the advantage of controlling the flatness in the dry state before as well as after processing without disadvantageously influencing the curling during drying. Indeed, it suflices to start with the desired amount of gelatin and to regu- 2,993,793 Patented July 25, 1961 late the proportion of gelatin and finely divided solid substances so that the layer will have the same drying speed as the emulsion layer and will exert in the dry state the same tensional forces.

The fillers in accordance with our invention are finely divided solid substances, for instance, insoluble mineral compounds, such as titanium dioxide, magnesium oxide, antimony oxide, aerogels or suspensions of finely divided silica, diatomaceous earth, lithophone, barium sulphate, barium wolframate, calcium carbonate, china clay, and asbestos, carbon black, organic substances, such as starch, hardened gelatin grains, and urea-formaldehyde resins. The particles must be smaller than 10 ,u, preferably. 1 to 0.01 whereby it is preferred in most cases that the refraotive index and the particle size of the inert substances be such that no matting efiect is obtained.

The amount of filling material used in our process Varies from 2 to calculated on the amount of gelatin present in the layer.

The incorporation of the filler into the gelatin layer and the application of the layer to the multilayer material are done in a way known in the art. The role the inert substances play appears clearly from the following experiments:

Both sides of a cellulose aceto-butyrate film of a thickness of 0.08 mm. are coated with a gelatin layer containing 10 gm. gelatin per sq. 111. One of the gelatin layers, however, contains 3 gm. of starch per sq. m. as very fine particles. The material shows before and after processing a curl toward the starch-containing layer, for instance, after treatment in the photographic developing and fixing baths. After drying, the curvature of the curl has a radius of 20 mm. Comparison material with no starch present was under otherwise identical circumstances practically fiat.

One side of a cellulose triacetate film is coated with a gelatin layer containing 15 gm. gelatin per sq. m. The rear is likewise coated with a gelatin layer containing only 10 gm. gelatin per sq. m., but also containing previously added 3 gm. BaSO Although the content of dry substance at the rear amounts to only 13 gm. per sq. m., this material still curls toward the rear, after treating in developing and fixing baths, and drying as usual.

The following examples are given to illustrate the way in which our invention can be put into practice in the photographic field. They are, however, by no means intended to limit the scope of the invention.

Example 1 The rear of a cellulose aceto-butyrate film coated with a high-contrast emulsion for graphic purposes is coated with a gelatin layer containing 25 gm. finely divided silica per 100 gm. gelatin. This material curls only slightly before and after processing, whereas a similar material with no silica showed a strong curl toward the emulsion layer. The presence of silica in the back layer does not influence adversely the transparency of said layer in the wet nor in the dry state.

Example 2 A negative film for studio photography is coated at the rear with a gelatin layer containing 20 gm. BaSO per 100 gm. gelatin. The film remains perfectly flat after processing and drying, and its curling is notably ameliorated before and during processing, compared with a photographic film bearing a pure gelatin anticurling layer.

Example 3 The BaSO of Example 2 was replaced by the same quantity of TiO The same improvement of the photo graphic material as to curling was observed.

' 3 Example 4 A negative photographic film is coated at the rear with a gelatin layer containing 10 gm. starch per 100 gm. gelatin. The film remains perfectly flat after processing and drying.

Example 5 To 100 parts of a 4% gelatin solution is added 1 part of a 15% suspension of a very finely divided asbestos. The suspension thus obtained is applied to the rear of a graphic material which, without back layer, after developing, fixing and drying unfavorably curls toward the image. After applying the back layer containing the asbestos, the material curls only slightly after finishing, with the image outside. It can be worked very easily.

It will be apparent that While we have described our invention in a few forms only, many changes and modifications may be made without departing from the spirit of the invention defined in the following claim.

We claim:

A photographic noncurling film including a transparent base bearing on one side at least one light-sensitive silver halide emulsion and on the other side a clear transparent gelatin layer containing finelydivided silica of an average particle size of 1 to 0.01 ,1 in an amount'between- 2 to 100% of the gelatin content of said layer.

References Cited in the file of this patent UNITED STATES PATENTS 1,479,939 Sulzer Jan. 8, 1924 1,597,727 De Sperati Aug. 31, 1926 1,631,421 Lohofer June 7, 1927 2,095,018 Wilmanns Oct. 5, 1937 2,143,791 Nadeau Jan. 10, 1939 2,322,037 Lindquist June 15, 1943 2,662,013 Sulech et al. Dec. 8, 1953 2,698,235 Swindells Dec. 28, 1954 

